Abstract Over 200,000 women undergo surgery for pelvic organ prolapse each year. One of the biggest current challenges is recurrent prolapse following surgery. At seven years, the failure rate for the ?gold standard? operation performed by expert surgeons in the NIH Pelvic Floor Disorders Network is 25%. While improvements in surgical management have led to better long-term outcomes for Level I (apical) support, emerging data indicate that Level III (genital hiatus) support is not addressed by Level I surgery and may be the most significant predictor of prolapse recurrence. Current progress is blocked by our lack of understanding regarding the specific anatomical defects that lead to recurrent prolapse, as well as our inability to identify women prior to surgery who are at high risk for recurrence. From a prior NIH-funded study, our research group has preoperative MRIs on 133 women who underwent surgery for prolapse, and for a subset of these we have limited clinical data about prolapse recurrence. Preliminary analyses of these data suggest that a novel preoperative MRI measure of the genital hiatus (?gh), which is the change in genital hiatus from rest to strain, may be associated with postoperative recurrence; however, our current sample size is too small to be able to conduct multivariable logistic regression. We seek funding to bring these women back for clinical exams to identify anatomical preoperative biomarkers responsible for prolapse recurrence and, for a subset, acquire postoperative MRI to identify structural failure sites. Pilot data from this study can then be used to power a larger, definitive study. AIM 1: Identify preoperative factors associated with recurrence: We hypothesize that the ability to maintain a closed genital hiatus (gh) will be a predictor of surgical success. Specifically, we propose a new variable to assess levator status, ?gh, which is the change in genital hiatus size from rest to strain. We expect women with a smaller preoperative ?gh to have a higher prevalence of recurrence. We will test the hypothesis that preoperative ?gh is a stronger predictor of surgical failure than existing measurements associated with levator ani muscles. AIM 2: Postoperative failure phenotyping: Acquire and compare postoperative Stress MRI for 10 women with recurrence versus 10 women with long-term success following prolapse surgery. a) We will identify structural failure sites on postoperative MRIs for women with anatomical recurrence following prolapse surgery. b) We will test the null hypothesis that there is no difference in Level III support measures between women with prolapse recurrence and those with long-term success.